Conformable retroreflective film structure

ABSTRACT

The present invention includes conformable retroreflective structures. In some embodiments, the conformable retroreflective structures are also shrink resistant. The conformable retroreflective structures include a transparent plasticized polyvinyl chloride film having a first side and a second side; a first transparent polymer layer overlying the first side of the plasticized polyvinyl chloride film; a second transparent polymer layer overlying the second side of the plasticized polyvinyl chloride film; an array of retroreflective cube-corner elements underlying the second transparent polymer layer; and a plasticizer resistant adhesive underlying the array of retroreflective cube-corner elements. In some embodiments, the first and second transparent polymer layers are transparent, radiation-cured polymer layers.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/728,722 filed Mar. 27, 2007, which claims the benefit of U.S.Provisional Patent Application No. 60/788,081, filed on Mar. 31, 2006,the entire teachings of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Retroreflective materials are employed for various safety and decorativepurposes. Particularly, these materials are useful at nighttime whenvisibility is important under low light conditions. With perfectretroreflective materials, light rays are reflected essentially towardsa light source in a substantially parallel path along an axis ofretroreflectivity. Retroreflective materials can be used as reflectivetapes and patches for clothing such as vests and belts. Also,retroreflective materials can be used on posts, barrels, traffic conecollars, highway signs, vehicles, warning reflectors, etc.Retroreflective material can include arrays of randomly oriented microndiameter spheres or close packed cube-corner (prismatic) arrays.

Cube-corner or prismatic retroreflectors are described, for example, inU.S. Pat. No. 3,712,706, issued to Stamm on Jan. 23, 1973, the teachingsof which are incorporated by reference herein. Generally, the prisms canbe made by forming a master negative die on a flat surface of a metalplate or other suitable material. To form the cube-corner elements,three series of parallel equidistance intersecting V-shaped grooves 60degrees apart are inscribed in the flat plate. The die is then used toprocess the desired cube-corner array into a rigid flat plastic surface.

Further details concerning the structures and operation of cube-cornermicroprisms can be found in U.S. Pat. No. 3,684,348, issued to Rowlandon Aug. 15, 1972, the teachings of which are incorporated by referenceherein. A method for making retroreflective sheeting is also disclosedin U.S. Pat. No. 3,689,346 issued to Rowland on Sep. 5, 1972, theteachings of which are incorporated by reference herein. For example,cube-corner microprisms can be formed in a cooperatively configuredmold. The prisms can be bonded to sheeting, which is applied thereoverto provide a composite structure in which the cube-corner elementsproject from one surface of the sheeting.

Adhesively mounted retroreflective materials are prone to wrinkling whenapplied to contoured surfaces. In some instances, it has been necessaryto cut a retroreflective structure to a specific geometry to preventwrinkles when the retroreflective structure was applied to a contouredsurface. In addition, many adhesively mounted retroreflective materialshave been susceptible to shrinkage. The problems of wrinkling andshrinkage have heretofore hindered the application of retroreflectivematerials to contoured surfaces.

SUMMARY OF THE INVENTION

The present invention includes conformable retroreflective structures.The conformable retroreflective structures include a transparentplasticized polyvinyl chloride film having a first side and a secondside; a first transparent polymer layer overlying the first side of theplasticized polyvinyl chloride film; a second transparent polymer layeroverlying the second side of the plasticized polyvinyl chloride film; anarray of retroreflective cube-corner elements underlying the secondtransparent polymer layer; and a plasticizer resistant adhesiveunderlying the array of retroreflective cube-corner elements. In someembodiments, the first and second transparent polymer layers aretransparent, radiation-cured polymer layers.

A “conformable” retroreflective structure can be adhered to contouredcurved surfaces of a substrate without the formation of significantwrinkles and, in some embodiments, can be adhered to contoured curvedsurfaces of a substrate without the need to cut the retroreflectivestructure to specific geometries to prevent wrinkles. “Conformable”refers to a property of the retroreflective structures. The presentinvention is not limited to retroreflective structures for applicationto any particular substrate geometry. For example, the conformableretroreflective structures of the present invention can be applied toflat, contoured, or curved substrates.

In some instances, the conformable retroreflective structures include atransparent plasticized polyvinyl chloride film having a first side anda second side; a first transparent, radiation-cured polymer layeroverlying the first side of the plasticized polyvinyl chloride film; asecond transparent, radiation-cured polymer layer overlying the secondside of the plasticized polyvinyl chloride film; an array ofretroreflective cube-corner elements underlying the second transparent,radiation-cured coating layer; a metallized reflective layer depositedon the array of retroreflective cube-corner elements; and a crosslinked,plasticizer-resistant acrylic adhesive bonded to the metallizedreflective layer.

In one aspect of the invention, a conformable retroreflective structureincludes a transparent plasticized polyvinyl chloride film having afirst side and a second side; a first transparent polyurethane layeroverlying the first side of the plasticized polyvinyl chloride film,wherein the first polyurethane layer has a thickness of about 0.0004 toabout 0.0009 inches (about 0.01 to about 0.023 mm); a second transparentpolyurethane layer overlying the second side of the plasticizedpolyvinyl chloride film wherein the second transparent polyurethanelayer has a thickness of about 0.0004 to about 0.0009 inches (about 0.01to about 0.023 mm); an array of retroreflective cube-corner elementsunderlying the second transparent, radiation-cured coating layer; and acrosslinked, plasticizer-resistant acrylic adhesive underlying the arrayof retroreflective cube-corner elements.

In some embodiments, the conformable retroreflective structures are alsoshrink resistant. “Shrink resistant,” as that term is used herein,refers to a property of a retroreflective structure wherein theretroreflective structure can substantially maintain its originaldimensions. In some embodiments, the retroreflective structures areshrink resistant and maintain their original dimensions even aftervarious types of use, for example, use in the outdoors.

Conformable retroreflective structures of the present invention can beused, for example, as a retroreflective vehicle graphics film forimproved nighttime vehicle conspicuity. In some embodiments, theconformable retroreflective structures can be applied to non-contouredor contoured curves of motor vehicles without creating substantialwrinkles or other aesthetic defects. In some instances, the conformableretroreflective structures are shrink resistant and do not experiencethe shrinkage normally associated with conventional adhesively mountedplasticized polyvinyl chloride based film products.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawing in which like reference characters refer to thesame parts throughout the different views.

The drawing is not necessarily to scale, emphasis instead being placedupon illustrating embodiments of the present invention.

The FIGURE is a cross sectional view of a retroreflective structureaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

Generally, the conformable retroreflective structures of the presentinvention include a transparent plasticized polyvinyl chloride filmhaving a first side and a second side; a first transparent polymer layeroverlying the first side of the plasticized polyvinyl chloride film; asecond transparent polymer layer overlying the second side of theplasticized polyvinyl chloride film; an array of retroreflectivecube-corner elements underlying the second transparent polymer layer;and a plasticizer resistant adhesive underlying the array ofretroreflective cube-corner elements.

The FIGURE illustrates an embodiment of the present invention.Conformable retroreflective structure 2 includes transparent plasticizedpolyvinyl chloride film 4. Suitable transparent plasticized vinyl filmscan be manufactured, for example, by calendaring, extrusion, solventcasting, or other methods known in the art. Polyvinyl chloride film 4can contain various colorants and performance additives well-known tothose of skill in the art. In one embodiment, the film is a calenderedfilm. Calendaring can be an especially useful method due to theflexibility of the calendaring process to compound colorants andperformance enhancement additives.

Polyvinyl chloride film 4 is substantially transparent. In someembodiments, Polyvinyl chloride film 4 is substantially transparent tovisible light. Polyvinyl chloride film 4 can be either clear ortransparently colored. In some embodiments, the polyvinyl chloride filmincludes a fluorescent dye.

Polyvinyl chloride film 4 can have a thickness, for example, of about0.001 to about 0.022 inches (about 0.025 to about 0.56 millimeters (mm))such as about 0.004 to about 0.020 inches (about 0.1 to about 0.51 mm),about 0.004 to about 0.01 inches (about 0.1 to about 0.25 mm), about0.006 to about 0.01 inches (about 0.15 to about 0.25 mm), or about 0.006to about 0.018 inches (about 0.15 to about 0.46 mm). The thickness ofthe base film can be selected based on the flexibility, tear resistance,and color stability desired for any particular application. Furthermore,the selected film thickness of the structure can be selected based onthe desired long-term weatherability characteristics of the structure.In general, thinner layers of polyvinyl chloride films are preferred.However, if the vinyl film is too thin, then the structure will lose itconformability because the prism stiffness will dominate. However, athinner finished product, and therefore a thinner vinyl film, isdesirable when improved flexibility and/or raw materials cost are moreimportant. For example, in preferred embodiments, the polyvinyl chloridefilm has a thickness about 0.004 to about 0.01 inches (about 0.1 toabout 0.25 mm), with a preferred range being from 0.004-0.02 inch,including but not limited to e 0.012-0.018 inch, with some possibilitythat decreased thickness is preferred as color stability of additivesimproves. The selected thickness can be important as it can affect theability of the retroreflective structure to conform to a contouredsurface. Furthermore, the thickness of the film can affect the long-termweatherability characteristics of the structure. Therefore, the selectedthickness of the transparent plasticized polyvinyl chloride film can bedetermined, for example, based on conformability and weatherabilityrequirements for any particular application.

The transparent plasticized polyvinyl chloride film has a Shore Ahardness, for example, of about 25 to about 60 such as about 30 to about50, about 30 to about 45, or about 35 to about 40. In one particularembodiment, the transparent plasticized polyvinyl chloride film has aShore A hardness of about 36. Shore A hardness is a measure of therelative hardness of a material and can be determined with an instrumentcalled a Shore A durometer.

Examples of suitable polyvinyl chloride film include a polyvinylchloride film available from American Renolit Corporation under thetrademark RENOLIT® (Whippany, N.J.), or a calendered plasticizedpolyvinyl chloride film available from Achilles USA, Everett, Wash.

In addition to transparent plasticized polyvinyl chloride film 4,conformable retroreflective structure 2 also contains at least twotransparent, polymer layers. Transparent plasticized polyvinyl chloridefilm 4 has a first side and a second side. First transparent polymerlayer 6 overlies the first side of plasticized polyvinyl chloride film4. “Overlies” and “overlying” refer to the relative orientation of thepolymer layer to the plasticized polyvinyl chloride film. In someembodiments, one or more layers of material lie between the firsttransparent polymer layer and the plasticized polyvinyl chloride film.In one particular embodiment, the first transparent polymer layer isdirectly attached to the plasticized polyvinyl chloride film. Secondtransparent polymer layer 9 underlies the second side of plasticizedpolyvinyl chloride film 4. “Underlies” and “underlying” refer to therelative orientation of the polymer layer to the plasticized polyvinylchloride film. In some embodiments, one or more layers of material liebetween the second polymer layer and the plasticized polyvinyl chloridefilm. In one particular embodiment, the second transparent polymer layeris directly attached to the plasticized polyvinyl chloride film.

First transparent polymer layer 6 and/or second transparent polymerlayer 8 can be formed from a formulation that includes a urethaneacrylate prepolymer. In one embodiment, a urethane acrylate prepolymer,e.g., a linear polyether urethane acrylate prepolymer, is the majoritycomponent of the formulation from which the transparent polymer layer isformed. In some instances, the molecular weight of the urethane acrylateprepolymer can be greater than about 1000 grams/mole such as, forexample, about 1000 to about 6000 grams/mole or about 2000 to about 4000grams/mole. The acrylate moiety functionality of the prepolymer can be,for example, about 1 to about 6. In a preferred embodiment, the desiredacrylate moiety functionality is about 1.2 to about 3. Functionalityrefers to the average number of reactive acrylate end groups permolecule. The polyurethanes can be aliphatic or aromatic. However,typically, aliphatic polyurethanes are preferred over aromaticpolyurethanes because retroreflective structures containing aliphaticpolyurethanes can have better weatherability characteristics. Thus, inone embodiment, first transparent polymer layer 6 and/or secondtransparent polymer layer 8 include an aliphatic polyurethane acrylate.

Suitable linear polyether urethane acrylate prepolymers include, but arenot limited to, BR5825, BR5824, BR582, BR543 and BR541 available fromBomar Specialties Co. (Winsted, Conn.).

The formulations for the transparent polymer layers also can containother prepolymers for such functions as viscosity modification, adhesionpromotion, tack reduction, and other purposes. Examples ofmonofunctional prepolymers that can be used for viscosity modificationinclude, but are not limited to, isobornyl acrylate; 2(2-ethoxyethoxy)ethyl acrylate; tridecyl acrylate; octyldecyl acrylate; 2-phenoxyethylacrylate; 2-phenoxyethyl methacrylate; alkoxylated lauryl acrylate;lauryl acrylate; lauryl methacrylate; isodecyl acrylate; stearylacrylate; and stearyl methacrylate. Examples of multifunctionalprepolymers that can be used for viscosity modification include, but arenot limited to, trimethylolpropane triacrylate; trimethylolpropanetrimethacrylate; ethoxylated trimethylolpropane trimethacrylate;propoxylated trimethylolpropane triacrylate; and propoxylated glyceryltriacrylate Additional prepolymers that can be used for additionalfunctional benefits include, but are not limited, to epoxy acrylates;brominated epoxy acrylates; polyester acrylates; silicone acrylates;fluoroacrylates; and polybutadiene acrylates.

First transparent polymer layer 6 and/or second transparent polymerlayer 8 can include a radiation-cured polymer, e.g., an ultraviolet (UV)cured polymer. In some embodiments, either or both of first transparentpolymer layer 6 and second transparent polymer layer 8 includeradiation-cured polyurethane such as, for example, UV-cured polyurethaneacrylate.

In some embodiments, one or more of the first and second transparentpolymer layers are radiation-cured. In general, a photoinitiator isneeded to cure a radiation-curable formulation. Examples ofphotoinitiators that can be used include, but are not limited to,benzyldimethylketal; 2-hydroxy-2-methyl-1-phenyl-1-propanone;alpha-hydroxycylohexylphenyl ketone; benzophenone;2,4,6-trimethylbenzoylphenyl phosphineoxide; isopropylthioxanthone,ethyl-4-dimethylamino benzoate; 2-ethyl-4-dimethyl amino benzoate; oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]; difunctionalalpha-hydroxy ketone; 1-[4-94-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl) propan-1-one;2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropane-1-one; phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide);2,2-dimethoxy-1,2-diphenylethan-1-one; 2,2-diethoxy-1-phenyl-ethanone;and combinations thereof.

In particular embodiments, the first and/or second transparentradiation-cured polymer layers are formed from compositions whichinclude aliphatic urethane acrylate prepolymer, monofunctional acrylateprepolymer, multifunctional acrylate prepolymer, and a photoinitiator ora blend of photoinitiators.

In some embodiments, either or both of first transparent polymer layer 6and second transparent polymer layer 8 include a solvent or water-basedpolyurethane. In some instances, first transparent polymer layer 6and/or second transparent polymer layer 8 include at least onepolyurethane selected from the group consisting of polyetherpolyurethanes, polyester polyurethanes, and polycarbonate polyurethanes.The polyurethanes can be aliphatic or aromatic. However, typically,aliphatic polyurethanes are preferred over aromatic polyurethanesbecause retroreflective structures containing aliphatic polyurethanescan have better weatherability characteristics.

Transparent polymer layers having aliphatic polyether polyurethane canbe made using various aliphatic diisocyanates such as, for example,isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), HMDI(HMDI being a 4,4′-dicyclohexylmethane diisocyanate) and tetramethylenexylene diisocyanate (TMXDI). Transparent polymer layers having aliphaticpolyester polyurethane can be made, for example, using any one ofnumerous polyester diols known in the art. Transparent polymer layershaving aliphatic polycarbonate polyurethane can be made, for example,using polycarbonate diols.

First transparent polymer layer 6 and second transparent polymer layer 8can have the same or different compositions. For example, firsttransparent polymer layer 6 can include any of the polymer compositionsdescribed supra while second transparent polymer layer 8 can include anyother polymer composition.

In one embodiment, the first transparent, radiation-cured polymer layerhas a thickness of about 0.0002 to about 0.001 inches (about 0.0051 toabout 0.025 mm). In other embodiments, the first transparent,radiation-cured polymer layer has a thickness of about 0.0004 to about0.0009 inches (about 0.01 to about 0.023 mm).

The second transparent, radiation-cured polymer layer can have athickness of about 0.004-0.009 inches.

In some embodiments, the retroreflective structure includes one or moretransparent polymer layers with a thickness of about 0.0001 inches (in.)(about 0.0025 mm) to about 0.0015 in. (about 0.038 mm), such as about0.0002 in. (about 0.0051 mm) to about 0.0013 in. (about 0.033 mm), about0.0002 in. (about 0.0051 mm) to about 0.001 in. (about 0.025 mm), about0.0005 in. (about 0.013 mm) to about 0.001 in. (about 0.025 mm), about0.0004 in. (about 0.01 mm) to about 0.0009 in. (about 0.023 mm), orabout 0.0007 in. (about 0.018 mm). The first and second transparentpolymer layers can have the same thickness or, in some instances, canhave different thicknesses.

The retroreflective structures of the present also include an array ofretroreflective cube-corner elements. Generally, retroreflectivestructure 2 includes array of retroreflective cube-corner elements 10underlying second transparent polymer layer 8. “Underlying” refers tothe relative orientation of the retroreflective cube-corner elements tothe second transparent polymer layer. In some embodiments, one or morelayers of material lie between the second transparent polymer layer andarray of retroreflective cube-corner elements.

Second transparent polymer layer can provide a substrate for the arrayof retroreflective cube-corner elements. In one embodiment, the array ofretroreflective cube-corner elements is attached to the secondtransparent polymer layer. Generally, the array of retroreflectivecube-corner elements has a window side exposed to incoming light raysand an opposite, facet side. The array of retroreflective cube-cornerelements can be oriented such that the window side faces the secondtransparent polymer layer. For example, window side of the array ofretroreflective cube-corner elements can be attached to the secondtransparent polymer layer. In some embodiments, the array ofretroreflective cube-corner elements is attached to the secondtransparent polymer layer using a transparent adhesive. Alternatively,the array of retroreflective cube-corner elements can be attached to thesecond transparent polymer layer using a transparent coating such as atransparent coating formed from a radiation-curable or solvent or waterbased coating formulation. In one embodiment, the array ofretroreflective cube-corner elements can be cast directly onto thesecond transparent polymer layer.

Array of retroreflective cube-corner elements 10 can be formed of apolymer, e.g., a substantially transparent polymer. After being formedinto the array of retroreflective cube-corner elements, the polymer ispreferably rigid, or substantially inflexible, at room temperature. Therigidity of the polymer in the array allows the cube-corner elements tomaintain their optical characteristics. The polymer can also benon-extensible, which is defined as not being capable of beingsubstantially stretched without breaking. The polymer can be selectedfrom a wide variety of polymers which include, but are not limited to,urethane, acrylic acid esters, cellulose esters, ethylenicallyunsaturated nitrites, hard epoxy acrylates, etc. Other polymers includepolycarbonates, polyesters and polyolefins, acrylate silanes, hardpolyester urethane acrylates. Other polymers, which are not as rigid,can also be used. These polymers include polyvinyl chloride andpolyvinylidene chloride. Preferably, the polymer is cast in a prismaticmold with a monomer or oligomer. The polymerization of the monomer oroligomer can be initiated by radiation, e.g., ultraviolet radiation.

In some embodiments, the array of retroreflective cube-corner elementscan be formed by methods such as those disclosed in U.S. Pat. No.3,684,348, issued to Rowland on Aug. 15, 1972; U.S. Pat. No. 3,689,346,issued to Rowland on Sep. 5, 1972; U.S. Pat. No. 3,811,983, issued toRowland on May 21, 1974; U.S. Pat. No. 3,830,682, issued to Rowland onAug. 20, 1974; U.S. Pat. No. 3,975,083, issued to Rowland on Aug. 17,1976; U.S. Pat. No. 4,332,847, issued to Rowland on Jun. 1, 1982; U.S.Pat. No. 4,801,193, issued to Martin on Jan. 31, 1989; U.S. Pat. No.5,229,882, issued to Rowland on Jul. 20, 1993; U.S. Pat. No. 5,236,751,issued to Martin, et al. on Aug. 17, 1993; U.S. Pat. No. 5,264,063,issued to Martin on Nov. 23, 1992; U.S. Pat. No. 5,376,431, issued toRowland on Dec. 27, 1994; U.S. Pat. No. 5,491,586, issued to Phillips onFeb. 13, 1996; U.S. Pat. No. 5,512,219, issued to Rowland on Apr. 30,1996; U.S. Pat. No. 5,558,740, issued to Bernard, et al. on Sep. 24,1996; U.S. Pat. No. 5,592,330, issued to Bernard on Jan. 7, 1997; andU.S. Pat. No. 5,637,173, issued to Martin, et al. on Jun. 10, 1997. Theentire contents of each patent are incorporated herein by reference.

The cube-corner elements of the array can have a length along eachcube-side edge, for example, in the range of about 0.0015 to about 0.02inches (about 0.038 to about 0.51 mm). Preferably, each cube-side edgehas a length of about 0.003 to about 0.008 inches (about 0.076 to about0.2 mm) such as about 0.0035 to about 0.006 inches (about 0.089 to about0.15 mm). In one embodiment, each cube-side edge has a length of about0.0035 inches (about 0.089 mm). In other preferred embodiments thisstructure uses prism of 0.006 inches; however, prisms of from0.0035-0.006 inches are in the working range.

The thickness of the array in the valleys where the cube-corner elementsintersect is preferably sufficiently thin so that the array can crackand split along the valleys when minimal force is applied to theretroreflective structure. In some embodiments, the thickness of thearray, which is the distance from the window side to apex of thecube-corner elements, is about 0.001 to about 0.009 inches (about 0.025to about 0.23 mm) such as about 0.001 to about 0.005 inches (about 0.025to about 0.13 mm), about 0.001 to about 0.003 inches (about 0.025 toabout 0.076 mm), or about 0.0015 to about 0.003 inches (about 0.038 toabout 0.076 mm). In one specific embodiment, the thickness of the arrayis about 0.0017 inches (about 0.043 mm). In this particular embodimentthe thickness of the array can be 0.0027 inches. However, prisms of from0.0017 to 0.0027 inches are in the working range.

In addition to the polyvinyl chloride film, the first and secondtransparent polymer layers, and the array of retroreflective cube-cornerelements, the retroreflective structures of the present invention alsoinclude an adhesive. Generally, retroreflective structure 2 includesadhesive 12 underlying array of cube-corner elements 10. “Underlying”refers to the relative orientation of the retroreflective adhesive tothe array of cube-corner elements.

Adhesive 12 can be applied to prism facets of the cube-corner elementsfor adhesion to optional substrate 14. If an adhesive is applieddirectly to the prism facets, however, the adhesive can cause thesurface of the prisms to wet, thereby destroying the air interface andreducing, or even eliminating, the ability of the prisms toretroreflect. As a result, a metallized reflective layer can be firstdeposited on the surface of the dihedral facets. Examples of suitablematerials for forming a reflective layer include, but are not limitedto, aluminum, silver, gold, palladium, and combinations thereof.Typically, the reflective layers are formed by sputtering or by vacuumdeposition. For example, the cube-corner elements can be vapor depositedwith aluminum to create a reflective metal layer. In one embodiment,aluminum is vapor deposited whereby aluminum is heated under a vacuumand aluminum vapor is condensed onto the cube-corner elements to form aaluminum layer, e.g., a continuous aluminum layer. Alternatively, metallacquers, dielectric coatings and other specular coating materials canbe employed to form a reflective layer on the cube-corner elements. Thethickness of the metallized reflective layer can be in the range ofabout 200 to about 600 Angstroms, for example, about 200 to about 500 orabout 200 to about 400 Angstroms. In one embodiment, adhesive is applieddirectly to a metallized reflective layer on the array ofretroreflective cube-corner elements. Thus, adhesive 12 can be bonded tothe metallized reflective layer.

Adhesive 12 can be selected based on its ability to adhesively bond toboth the array of cube-corner elements, e.g., an array of metallizedcube-corner elements, and a substrate. In addition, the adhesive shouldprovide enough adhesive strength such that the retroreflective structuredoes not separate from the substrate. Since the retroreflectivestructure of the present invention includes a plasticized polyvinylchloride film, plasticizer migration through the structure can be aconcern.

Typically, upon exposure to extended lengths of time and/or temperature,plasticizer will migrate from a plasticized polyvinyl chloride film.Such plasticizer can then enter the adhesive of a retroreflectivestructure and compromise its adhesive properties. The ability of theadhesive to maintain its adhesive properties after the retroreflectivestructure is subjected to extended lengths of time and/or temperature isan important consideration. The migration of plasticizer into theadhesive can weaken the adhesive properties such as adhesive andcohesive strength. Furthermore, plasticizer migration can causeshrinkage of the retroreflective structure and affect its dimensionalstability.

Accordingly, in one embodiment, adhesive 12 is plasticizer-resistant. Inanother embodiment, adhesive 12 is also a pressure sensitive adhesive.

Adhesive 12 can include silicone adhesives and/or acrylic adhesives suchas, for example, acrylic-based pressure sensitive adhesives or siliconepressure sensitive adhesives. In one preferred embodiment, the adhesiveis an acrylic-based adhesive due to acrylic adhesives' generally wideavailability and relatively low cost. In general, acrylic adhesives haveexcellent UV resistance, excellent resistance to non-polar solvents andtherefore make an excellent choice for this application. However, notall acrylic adhesives are suitably resistant to plasticizer migration.The compatibility of the adhesive determines the rate of plasticizermigration and the amount of plasticizer migration. In general, a lowadhesive polarity is thought to decrease the compatibility with a polarvinyl plasticizer. The polarity can be influenced by the monomers usedto manufacture the adhesive. Another method to decrease the plasticizermigration is by crosslinking the adhesive. Crosslinking is thought todecrease plasticizer solubility in the adhesive and thus substantialimproves the adhesive's performance. Either or both of these mechanismsfor improving plasticizer resistance can be employed in the presentinvention. In some instances, reducing plasticizer migration into theadhesive has had a dramatic effect on reducing shrinkage of theretroreflective structure.

In one aspect of the invention, the adhesive is selected from the groupconsisting of plasticizer-resistant silicone adhesives andplasticizer-resistant acrylic adhesives. In one preferred embodiment,the adhesive is a crosslinked plasticizer-resistant acrylic adhesive. Inanother embodiment, the adhesive has a low polarity as compared to theplasticizer present in the polyvinyl chloride film.

One example of a suitable adhesive was obtained from Scapa NorthAmerica, (Unifilm UV201; Windsor, Conn.). Another example of a suitableadhesive was obtained from Syntac Coated Products, LLC (Product No.06-1313D; Bloomfield, Conn.). Product No. 06-1313D from Syntac is ablend of high cohesive strength acrylic adhesive and a acrylic adhesivewith good adhesive strength.

The thickness of the adhesive can be, for example, about 0.002 in.(about 0.051 mm) to about 0.008 in. (about 0.2 mm) such as about 0.002in. (0.051 mm) to about 0.006 in. (about 0.15 mm), about 0.002 in.(0.051 mm) to about 0.005 in. (0.13 mm), about 0.001 in. (about 0.025mm) to about 0.003 in. (about 0.076 mm), or about 0.002 inches (about0.051 mm).

In some instances, the retroreflective structure can also include aprinting ink, such as an opaque white printing ink. A printing ink canbe included in the retroreflective structures, for example, to helpachieve appropriate Cap Y to meet industry whiteness specifications.Printing ink can be applied, for example, between polyvinyl chloridefilm 4 and second transparent polymer layer 8. Alternatively, printingink can be applied between the second transparent polymer layer and thearray of retroreflective cube-corner elements. For example, printing inkcan be applied between second transparent polymer layer 8 and array ofretroreflective cube-corner elements 10. Printing ink can enhance Cap Yperformance, however, it also can reduce the retroreflectivity of theprisms it covers. Therefore, the printing ink is often non-continuous.The printing ink can take various forms. For example, the printing inkcan be in the form of a pattern, logo, lettering, etc. In someembodiments, the printing ink has been applied using a screen printingmethod.

In some embodiments, a retroreflective structure includes a transparentplasticized polyvinyl chloride film having a first side and a secondside; a first transparent polymer layer overlying the first side of theplasticized polyvinyl chloride film; a second transparent polymer layeroverlying the second side of the plasticized polyvinyl chloride film; anon-continuous white opaque printed layer between the transparentplasticized polyvinyl chloride film and the second transparent polymerlayer or between the second transparent polymer layer and an array ofretroreflective cube-corner elements; the array of retroreflectivecube-corner elements underlying the white opaque printed layer; and aplasticizer resistant adhesive underlying the array of retroreflectivecube-corner elements.

In another embodiment, retroreflective structures of the presentinvention include a transparent plasticized polyvinyl chloride filmhaving a first side and a second side; a first transparent polymer layerattached to the first side of the plasticized polyvinyl chloride film; asecond transparent polymer layer attached to the second side of theplasticized polyvinyl chloride film; a non-continuous white opaqueprinted layer between the transparent plasticized polyvinyl chloridefilm and the second transparent polymer layer or between the secondtransparent polymer layer and an array of retroreflective cube-cornerelements; the array of retroreflective cube-corner elements underlyingthe white opaque printed layer; a metallized reflective layer formed onthe retroreflective cube-corner elements, and a plasticizer-resistantadhesive bonded to the metallized reflective layer.

Suitable transparent plasticized polyvinyl chloride films, transparentpolymer layers, arrays of retroreflective cube-corner elements,metallized reflective layers, and plasticizer-resistant adhesive, aredescribed supra.

In one aspect, the present invention includes a transparent plasticizedpolyvinyl chloride film having a first side and a second side; a firsttransparent polymer layer overlying the first side of the plasticizedpolyvinyl chloride film; a second transparent polymer layer overlyingthe second side of the plasticized polyvinyl chloride film; an array ofretroreflective cube-corner elements underlying the second transparentpolymer layer; a polymeric film layer sealed through the array ofcube-corner elements to the second transparent polymer layer. Sealing isprovided through both the prisms and the transparent polymer layer downto the transparent plasticized PVC film.

A plasticizer resistant adhesive is then bonded to the polymeric filmlayer. The polymeric film layer can be, for example, a plasticizedpolyvinyl chloride film. The composition of such a polymeric film layercan be similar to transparent plasticized polyvinyl chloride film 4described supra. Polymeric film layer, however, can be transparent oropaque. Polymeric film layer can be sealed through the array ofcube-corner elements to the second transparent polymer layer throughtechniques such as, for example, radio frequency or ultrasonic sealingor welding. In some embodiments, such a polymeric film layer caneliminate any need for metallization of the array of retroreflectivecube-corner elements.

The retroreflective structures of the present invention can also includea substrate bonded to the adhesive. The substrate can include anysurface to which it is desired to attach a retroreflective structureincluding, but not limited to, fabrics, metals, plastics, and wood.

A method for manufacturing a conformable retroreflective structureincludes attaching first and second transparent polymer layers on thefirst and second sides of a transparent plasticized polyvinyl chloridefilm. In one embodiment, a radiation-curable transparent polymer layerformulation is applied to the plasticized polyvinyl chloride film andthe formulation is cured using radiation, e.g., ultraviolet radiation.Optionally, a non-continuous white opaque printing ink can be sandwichedbetween a transparent polymer layer and the plasticized polyvinylchloride film or can be sandwiched between the second transparentpolymer layer and the array of retroreflective cube-corner elements.Then, the array of retroreflective cube-corner elements can bepositioned to underlie to one of the transparent polymer layers. In someembodiments, a metallized reflective layer is deposited on the array ofretroreflective cube-corner elements. Finally, a plasticizer-resistantadhesive is applied to underlie the array of retroreflective cube-cornerelements. For example, a plasticizer-resistant adhesive can be appliedto a metallized reflective layer.

In another method for manufacturing a retroreflective structure, a firsttransparent polymer layer, e.g., a radiation-cured transparent polymerlayer, is applied to a first side of a transparent plasticized polyvinylchloride film. Then, a second transparent polymer layer, e.g., aradiation-cured transparent polymer layer, is applied to a second sideof a transparent plasticized polyvinyl chloride film. A non-continuouswhite opaque printing ink can then be attached to the second transparentpolymer layer. An array of retroreflective elements with a metallizedreflective layer can be then attached to underlie the white opaqueprinting ink. Lastly, a plasticizer-resistant adhesive is coated overthe metallized reflective layer.

EXAMPLE 1

A 0.01 in. (about 0.25 mm) plasticized polyvinyl chloride film wascoated with a 0.0007 in. (about 0.018 mm) radiation-cured polymer on itsfirst side. The formulation of the coating included 53.3 weight percent(wt %) of a linear polyether urethane acrylate prepolymer with 2.4functionality and a viscosity of 150,000 cP at 50° C.; 10 wt % of anethoxylated-3-trimethylolpropane triacrylate; 28.5 wt. % isobornylacrylate; 5 wt % 1-hydroxy-cyclohexyl-phenyl-ketone photoinitiator; and3.2 wt % of a photoinitiator consisting of a blend of 50 wt % 2,4-6-trimethylbenzoyl-diphenyl-phoshineoxide and 50 wt %2-hydroxy-2-methyl-1-phenyl-propan-1-one. Additionally, the film wascoated with a second 0.0007 in. (about 0.018 mm) radiation-cured coating(the same coating formulation as mentioned previously) on the sideopposite the first side. A non-continuous pattern of radiation curedscreen print layer was attached to the second radiation-cured coating.An array of retroreflective cube corner elements was attached to theradiation-cured screen print layer. A layer of metallized aluminum wasattached to the retroreflective cube-corner elements. A plasticizerresistant acrylic based adhesive with a thickness of 0.002 in. (about0.051 mm) was applied to the metallized retroreflective cube-cornerelements. The laminated sample was cut to dimensions of roughly 8-inchesby 8-inches (about 20 centimeters (cm) by 20 cm). The sample wasadhesively laminated to an aluminum panel by using a pressure of25-lbs/linear inch The sample was measured for dimension in bothcoordinates, labeled the machine direction (“MD”) and the transversedirection (“TD”). The laminated sample was then placed in a 150° F.(about 66° C.) oven and the dimensions were measured at time intervalsof 14 days, 21 days, and 28 days. Table 1 shows the percentage change indimension for the machine direction (“MD”) and the transverse direction(“TD”).

TABLE 1 14-days 14-days 21-days 21-days 28-days 28-days (MD) (TD) (MD)(TD) (MD) (TD) Percent 0.18% 0.24% 0.37% 0.24% 0.37% 0.36% Change inDimension

After approximately 28 days of 150° F. (about 66° C.) heat exposure, theretroreflective structure exhibited a low degree of shrinkage.

EXAMPLE 2

A 0.01 in. (about 0.25 mm) plasticized polyvinyl chloride film wascoated with a 0.0006 in. (about 0.015 mm) radiation-cured polymer on itsfirst side. The formulation of the coating included 55.3 weight percent(wt %) of a linear polyether urethane acrylate prepolymer with 2.4functionality and a viscosity of 150,000 cP at 50° C. and a molecularweight of between 2000 and 4000 grams per mole; 3 wt % of andipentaerythritol pentaacrtyle; 36.7 wt. % isobornyl acrylate; 3 wt %1-hydroxy-cyclohexyl-phenyl-ketone photoinitiator; and 2 wt % of aphotoinitiator consisting of a blend of 50 wt %2,4-6-trimethylbenzoyl-diphenyl-phoshineoxide and 50 wt %2-hydroxy-2-methyl-1-phenyl-propan-1-one. Additionally, the film wascoated with a second 0.0006 in. (about 0.015 mm) radiation-cured coating(the same coating formulation as mentioned previously) on the sideopposite the first side. An array of retroreflective cube cornerelements was attached to the second radiation-cured screen coatinglayer. A plasticizer resistant acrylic based adhesive with a thicknessof 0.002 in. (about 0.051 mm) was applied to the retroreflectivecube-corner elements. The laminated sample was cut to dimensions ofroughly 95 mm×95 mm (about 3.74 inches (in) by 20 in). The sample wasadhesively laminated to a Ford waterbased painted steel panel utilizinga Ford waterbase paint system by using a pressure of 73-lbs/square inch[3,495 Pa]. The sample was measured for dimension in both coordinates,labeled the machine direction (“MD”) and the transverse direction(“TD”). The laminated sample was then placed in a 150° F. (about 66° C.)oven and the dimensions were measured after 8-days. Table 1 shows thepercentage change in dimension for the machine direction (“MD”) and thetransverse direction (“TD”).

EXAMPLE 3

The same as example 1 except the plasticized polyvinyl chloride film wascoated on both surfaces with a different formulation. The formulation ofthe coating included 65 weight percent (wt %) of a linear polyetherurethane acrylate prepolymer with 2.0 functionality and a viscosity of35,000 cP at 50° C. and a molecular weight of less than 2000 grams/mole;30 wt. % of isobornyl acrylate; 3 wt %1-hydroxy-cyclohexyl-phenyl-ketone photoinitiator; and 2 wt % of aphotoinitiator consisting of a blend of 50 wt % 2,4-6-trimethylbenzoyl-diphenyl-phoshineoxide and 50 wt %2-hydroxy-2-methyl-1-phenyl-propan-1-one.

COMPARATIVE EXAMPLE 1

The same as example 1 except the plasticized polyvinyl chloride film wasnot coated on both surfaces.

8-days (MD) 8-days (TD) Example 1 0.32% 0.26% Example 2 0.39% 0.29%Comparative Example 1 1.10% 1.00%It can be seen from the examples that the addition of the radiationcured coatings to the retroreflective structure reduces the amount ofshrinkage of the structure significantly. It was unanticipated that thatthe radiation cured polymer coating would reduce the overall shrinkageof the structure.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A conformable retroreflective structure, comprising: a) a transparentplasticized polyvinyl chloride film having a first side and a secondside; b) a first transparent polymer layer overlying the first side ofthe plasticized polyvinyl chloride film; c) a second transparent polymerlayer overlying the second side of the plasticized polyvinyl chloridefilm; d) an array of retroreflective cube-corner elements underlying thesecond transparent polymer layer; and e) a plasticizer-resistantadhesive underlying the array of retroreflective cube-corner elements.2. The retroreflective structure of claim 1 wherein the transparentplasticized polyvinyl chloride film has a thickness of about 0.004 toabout 0.1 inches (about 0.01 to about 2.5 mm).
 3. The retroreflectivestructure of claim 1 wherein the transparent plasticized polyvinylchloride film has a thickness of about 0.012 to about 0.018 inches(about 0.35 to about 0.46 mm).
 4. The retroreflective structure of claim1 wherein the transparent plasticized polyvinyl chloride film includes afluorescent dye.
 5. The retroreflective structure of claim 1 wherein thefirst transparent polymer layer has a thickness of about 0.0002 to about0.001 inches (about 0.0051 to about 0.025 mm).
 6. The retroreflectivestructure of claim 1 wherein the first transparent polymer layer has athickness of about 0.0004 to about 0.0009 inches (about 0.01 to about0.023 mm).
 7. The retroreflective structure of claim 1 wherein thesecond transparent polymer layer has a thickness of about 0.0002 toabout 0.001 inches (about 0.0051 to about 0.025 mm).
 8. Theretroreflective structure of claim 1 wherein the second transparentpolymer layer has a thickness of about 0.0004 to about 0.0009 inches(about 0.01 to about 0.023 mm).
 9. The retroreflective structure ofclaim 1 wherein the first and second transparent polymer layers includean aliphatic polyurethane acrylate.
 10. The retroreflective structure ofclaim 1 wherein the first and second transparent polymer layers areformed from compositions which include aliphatic urethane acrylateprepolymer, monofunctional acrylate prepolymer, multifunctional acrylateprepolymer, and a photoinitiator or a blend of photoinitiators.
 11. Theretroreflective structure of claim 1 wherein the plasticizer-resistantadhesive is selected from the group consisting of silicone adhesives andacrylic adhesives.
 12. The retroreflective structure of claim 1 whereinthe plasticizer-resistant adhesive is a crosslinked,plasticizer-resistant acrylic adhesive.
 13. The retroreflectivestructure of claim 1 wherein the plasticizer-resistant adhesive has athickness of about 0.002 to about 0.005 inches (about 0.051 to about0.13 mm).
 14. The retroreflective structure of claim 1 wherein theplasticizer-resistant adhesive has a thickness of about 0.001 to about0.003 inches (about 0.025 to about 0.076 mm).
 15. The retroreflectivestructure of claim 1 wherein the array of retroreflective cube-cornerelements is coated with a metallized reflective layer.
 16. Theretroreflective structure of claim 15 wherein the metallized reflectivelayer includes a metal selected from the group consisting of aluminum,silver, gold, and palladium.
 17. The retroreflective structure of claim15 wherein the plasticizer-resistant adhesive is bonded to themetallized reflective layer.
 18. The retroreflective structure of claim1 further including a polymeric film layer sealed through the array ofretroreflective cube-corner elements and the second transparent polymerlayer to the plasticized polyvinyl chloride layer.
 19. Theretroreflective structure of claim 18 wherein the plasticizer resistantadhesive is bonded to the polymeric film layer.
 20. The retroreflectivestructure of claim 1 further including an opaque layer of ink.
 21. Theretroreflective structure of claim 20 wherein the opaque layer of ink isnon-continuous.
 22. The retroreflective structure of claim 20 whereinthe opaque layer of ink lies between the transparent plasticizedpolyvinyl chloride film and the second transparent polymer layer. 23.The retroreflective structure of claim 20 wherein the opaque layer ofink lies between the transparent plasticized polyvinyl chloride film andthe array of retroreflective cube-corner elements.
 24. A conformableretroreflective structure, comprising: a) a transparent plasticizedpolyvinyl chloride film having a first side and a second side; b) afirst transparent polymer layer overlying the first side of theplasticized polyvinyl chloride film, wherein the first transparentpolymer layer has a thickness of about 0.0004 to about 0.0009 inches(about 0.01 to about 0.023 mm); c) a second transparent polymer layeroverlying the second side of the plasticized polyvinyl chloride filmwherein the second transparent polymer layer has a thickness of about0.0004 to about 0.0009 inches (about 0.01 to about 0.023 mm); d) anarray of retroreflective cube-corner elements underlying the secondtransparent polymer layer; and e) a plasticizer-resistant acrylicadhesive underlying the array of retroreflective cube-corner elements.25. The conformable retroreflective structure of claim 24 wherein thefirst transparent polymer layer includes at least one polymer selectedfrom the group consisting of polyurethane, polyether polyurethanes,polyester polyurethanes, and polycarbonate polyurethanes.
 26. Theconformable retroreflective structure of claim 24 wherein the firsttransparent polymer layer is a radiation-cured layer of polyurethaneacrylate.
 27. The conformable retroreflective structure of claim 24wherein the second transparent polymer layer includes at least onepolymer selected from the group consisting of polyurethane, polyetherpolyurethanes, polyester polyurethanes, and polycarbonate polyurethanes.28. The conformable retroreflective structure of claim 24 wherein thesecond transparent polymer layer is a radiation-cured layer ofpolyurethane acrylate.
 29. A method for manufacturing a conformableretroreflective structure, comprising: a) attaching a first transparentpolymer layer on a first side of a transparent plasticized polyvinylchloride film; b) attaching a second transparent polymer layer on asecond side of the transparent plasticized polyvinyl chloride film; c)positioning an array of retroreflective cube-corner elements to underliethe second transparent polymer layer; and d) applying aplasticizer-resistant acrylic adhesive to underlie the array ofretroreflective cube-corner elements.
 30. The method of claim 29 furtherincluding depositing a metallized reflective layer on the array ofretroreflective cube-corner elements.
 31. The method of claim 30 whereinthe plasticizer-resistant acrylic adhesive is applied to the metallizedreflective layer.
 32. The method of claim 29 further includingsandwiching an opaque layer of ink between the first transparent polymerlayer or the second transparent polymer layer and the transparentplasticized polyvinyl chloride film.
 33. The method of claim 29 furtherincluding sandwiching an opaque layer of ink between the secondtransparent polymer layer and the array of retroreflective cube-cornerelements.